Busy-test circuit for telephone cord circuits



Aug. 4, 1925.

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BUSY TEST CIRCUIT FOR TELEPHONE CORD CIRCUITS Filed 541gi 15, 1923 l Le@ l [fas'mtanm Qld-lin.:

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Patented ug. 4, 1925.

UNITED' STATES PATENTv OFFICE.

EG-INHARD DIETZE, OF BROOKLYN, NEW YORK, .ASSIGNOR TO AMERICAN TELEPHONE AND TELEGBAPI-I COMPANY, A CORPORATION 0F NEW YORK.

BUSY-TEST GIRCUITFOR TELEPHONE CORD CIRCUITS.

Application led August 15, 1923; Serial No. 657,581.

To all whom t may concern.'

' Be it known that I, EGINHARD DIETZE, residing at Brooklyn,.in the county of Kings and State of New York, have invented certain Improvements in Busy-Test Circuits for Telephone Cord Circuits, of which the following is a specification.

This invention relates to telephoneoperators cord circuits, and more particularly to arrangements associated therewith by means of which tests may be made to determine the busy or idle condition of telephone lines termina-ting at telephone 'switchboards In practicey it has been customary in the smaller telephone exchanges, .wherethe use of repeating coils in the cord circuits would not be justified because of thehigh expense involved, to use special induction coils which are provided .in connection with the operators sets. These induction coils have had their windings grounded at midpoints and considerable vdifficulty has been experienced on account of noise' created in the operators receiver, especially during the period the jack of a line was being tested to determine its busy or idle condition. This disturbance by noise is caused by induction created between the telephone lines and parallel high power lines. Accordingly, it is an object of this invention to provide a busy test circuit in connection with cord 'circuits which will eliminate the inductive ,noises l in the operators receiver during the period of testing in a simple and inexpensive manner. y

The invention may be now more fully understood from the following description, when considered in connection with the accompanying drawing.

Referring to the drawing, Figure 1 illustrates diagrammatically such .portions of cord circuits and associated operators telephone set as are necessary for the purposes of this invention. This figure indicates the improved arrangement as applied to a common battery switchboard having a number of operators positions. F ig. 2 represents a modification of the operators telephone set as applied to a local battery switchboard.

In the drawing the numerals 1 and 2 designate cord circuits which have their sleeve conductors connected to battery, and which terminate, respectively, in plugs 3 and 4. The lugs 3 and 4 are adapted to be associated) with multiple jacks 5 and 6 which are' interconnected by a sleeve conductor 7. An operators set 8 is indicatedl as enclosed by dotted lines and connected with the cord circuits 1 and 2. Plug 3 is shown as applied to the jack 5 for the purpose of making-a busy test, and plug 4 is inserted in jack 6 for completing a call over the line 9. 10 indicates a power line paralleling the telephone line 9, said telephone line 9 having leakages shown by resistances to ground spaced at equal intervals. The positive "charge on the power line induces 'correspending negative charges on the telephone conductors. This permits current to=flow from the power line over the telephone line introducing noise in the operators receiver under the old arrangements. The current flow at the instant represented in thesketch is indicated by arrows.

In the operation of the improved circuit, assuming that a connection is desired with a station associated with the telephone line 9, the operator will select an idle cord circuit, for instance, the cord circuit 2. If, upon testing the wanted line by applying the tip 'conductor of the plug 4 to the sleeve of the jack 6 and depressing key 11, no busy indication lis produced in the operators receiver 12,'the plug 4 is inserted in said jack and a talking connection established over the tip land ring conductors of the cord circuit and the line 9 extending to the'called station in the usual manner. v

If an addtional connection Awith the telephone line comprising the conductors 9 1s desired during the period plug 4 is assostance, jack 5, the following circuit is closed: from battery, sleeve conductor 13, sleeve contacts of plug 4 and jack 6, sleeve conductor 7, sleeve contacts of jack 5, tip contact of plug 3, tip conductor of cord circuit 1, upper closed contact of key 14, talking conductor 15, through the operators listening means 12 to the opposite pole of the battery through a network comprising a high resistance 16 and a condenser 17 in parallel therewith. The closure of this circuit causes the sleeves of the busy line to be raised to a potential opposite to that of the tip of the connected cord circuit, resulting in the condenser 17 being charged when the tip of plug 3 is touched to the sleeve of jack 5. When the tip of plug 3 1s removed `from the sleeve of jackA 5, thecondenser 17 discharges through' the high resistance 16, which is shunted around it. The discharge of the condenser 17 produces a distinctive setuid or clic'li in the op'erators receiver which servesv as an indication to the operator that the line -is in use. The provision of the high resistancev serves' to reducev the current flowing through the receiver Y12, and is proportioned to give the proper click volume and prevent excessive noise therein.

An inductioncoil 18,- having primary and secondary windings, is associated with the operators vtelel'jhone set. rl`he receiver' 12 has one of its terminals connected through the midpointl or the secondary windings to the ring conductors or' the cord circuits while the .Y other terminal ot the receiver is connected to the tip conductors of the cord circuits. A resistance 19 is incorporated in the coil 18 for the purpose of so balancing the line that the transmitter which is associatedP with the primary windings of the coil 1.8 has no eiiect on the receiverv19 during the period it is in use. The transmitter has" one terminal connected tov battery through the retardation coil 20, as shown inFig. 1,` while in the modification indicated in Fig. 2 the battery isconnected di'- rectly inpseries with the transmitter.

From the above it will be apparent that bymeans of the improved metallic busy test circuit of this invention any interference which may arise, due to induction caused by oppositey charges of current between a telephone line and a parallel high power line; is entirely eliminated from the operatorsreceiver. l

While the arrangements of this invention have.' .been illustrated as embodied in certain specific forms which have been deemed de- 'sir'able it `will, bewunderstoo'd that they are capable of embodiment in many and Widely variedtorms without departing' from the spirit of th'e invention as deiinedl inthe appended claims.,

What is claimed is; 1

1.I A test circuit for an operators cord circuit Acomprising an operators listening In'eans having one terminal associated with the tip conductor or the cord, an ungrounded battery having one terminal connected to the other terminal di said listening means and another terminal connected to the sleeve conductorA of the cord, and a network in circuit 'with the' battery comprising a high resistance anda condenser in parallel therewith for reducing the flow of current through said listening means. p

2. A test circuit for` cord circuits comprising an operatorisl listening means having one terminal associated with the' tip conductor of the cord, an ungrounded! battery having one terminal connected to the other terminal or said listening means, a plurality ofsets of jacks with which said cord circuits may be associated, a sleeve conductor for interconnecting `each set of jacks, and means interposed between said listening means and said battery for causing said listening means to operate in a distinctive manner upon the application of the tip terminal t-o one `of said jacks when an associated jack of the setis busy. w

In a telephone svvitchboard,a ,plurality of subscribers lines terminatingv multipled jacks thereat,4 a sleeve conductor'for connecting Leach of. said' jacks lor a line, a plurality of cord circuits adapted to be4 aslsociated with said jacks, said oo-rd circuits including tip, -ring and sleeve conductors, listeningmean's associated .with the tip and ring conductors ofsa'id co1.'ds,an ungrounded battery having one terminal connected to the sleeve conductors of said cords, and means connected to the other terminal, of the battery and one terminal oit the listeningmeans responsive to the application of the tip conductor of a cord circuit to a busy jack for causing the listening means to operate in a distinctive manner.

In testimony whereof, I haveusi'gned m name to this specification this 3rd day of Aiugust, 1928. 

